Split-Hopkinson Pressure Bar (SHPB) method is the most versatile technique to evaluate the stress-strain relations of materials at high rate of strain. Over the decades, the method has been improved and developed, and now, it has been widely applied to investigate the various kinds of mechanical properties of materials under impact loading. Recent research activities and techniques related to this famous method are reviewed in the present paper.

View full abstract

In order to examine the impact behavior of mercury, which is one of important key-issues in a facility for high intensity neutron sources, the falling and colliding profiles of mercury droplets were recorded by high-speed video recorder. The impact force was also measured using the strain gage glued on an elastic bar. The falling mercury droplet oscillated between a prolate spheroid and an oblate one, repeatedly. The regathering and jumping of mercury at the collision point on the impact face of the target were observed after impact because of the strong surface tension of mercury. The impact force of mercury droplet was in proportion to the impact velocities and the square root of the potential energy. Since the non-dimensional duration time K that obtained experimentally is independent of the impact velocity and the size of the droplet, the mean applied stress due to the mercury droplet against the target is easily, predictable by the equation using K value and the impact velocity is known.

View full abstract

High velocity tensile behavior of structural materials is essential to design impact-resistant structure. In case of automotive body, especially of energy absorbing members such as front side members, dynamic behavior of thin plate plays a key role to eyaluate their energy absorbing ability. So far, dynamic tensile mechanical properties of thin plate have not attracted impact researchers' and engineers' attention very much, exceptfor laminated composite materials. In this paper, with the one bar method that is known as an effective high velocity tensile testing technique for cylindrical specimen of various solid materials, the previous thin plate spccimen assembly was improved for steels and aluminum alloys. The most important factor is fastening technique between an impact block and the assembly. Because, we fOrmerly fastened them with a pin in order to allow slight misalignment of the assembly of the previous design. This pin fastening introduced a tremendous initial peak on stress-strain curves, even for aluminum alloys. A new assembly fastened by a screw solves this problem drastically. Stress-strain curves obtained by the one bar method, with the new specimen assembly, are almost equivalent to those obtained by the tensile version of the split Hopkinson pressure bar method.

View full abstract

Split-Hopkinson pressure-bar technique has been widely adopted to evaluate dynamic constitutive relations for various kinds of materials. However, due mainly to a rectangular incident stress pulse with a short rising time, the strain rate becomes considerably higher when a difference in mechanical impedance between a specimen and the pressure bars is large. This tendency may be enhanced when determining strength of specimen because the incident pulse amplitude must be high enough to break a specimen. In this study, stepped and tapered striker bars were proposed to increase the rising time of incident stress pulse. A simple procedure was developed for simulating an incident stress pulse profile generated by a striker bar with variable cross section. Validation was done by comparing predicted incident stress pulse profiles of uniform, 5-stepped and tapered striker bars with those obtained by longitudinal impact experiments. In addition, four kinds of polymer specimens were tested by the three kinds of striker bars. Results showed that the strain rates at failure obtained by the 5-stepped and tapered striker bars were remarkably lower than that obtained by the uniform striker bar regardless of the material properties of specimen.

View full abstract

In a mercury target installed in a neutron scattering facility, pressure waves are induced by rapid heat deposition due to the injection of MW-class pulsed proton beam. It has been analytieally reported that the pressure waves impose large loads on the target vessel wall (structural body) and the negative (tensile) pressure is generated near the target beam window by coupled behavior between the deformation of the structural body and liquid mercury. The negative pressure may cause a cavitation bubble and the bubble collapse may cause damages such as pitting on the beam window. Impact tests were carried out by using the cylinder vessel filled with water to examine the coupled behavior between the structural body and liquid under impact loading. The thickness of a simulated beam window (the structural body) set on the bottom of the cylinder vessel and the impact velocity were varied to investigate conditions for the negative pressure-wave generation. The thinner the thickness and the higher the impact velocity, the negative pressures generate more readily because of the inertia effect of the deformed beam window by impact pressure. Additionally, FEM analyses were carried out to investigate the behavior of interface between the structural body and liquid.

View full abstract